Том 12, № 2 (2018)

The composition and structure of complexes that formed in aqueous solutions of trifluoroacetic acid were studied by frustrated multiple total internal reflection IR spectroscopy (FMTIR). Two types of complexes with a molecular structure formed: trimers CF₃COOH · (H₂O)₂ and cyclic tetramers (CF₃COOH)₂ · (H₂O)₂, in which the molecules of the components are arranged in pairs. In the range of acid concentrations from 100% to [H₂O]/[CF₃COOH] = 1: 1, only these tetramers formed, and all added water was bound into these hydrates. In more dilute solutions (up to [H₂O]/[CF₃COOH] = 2: 1), CF₃COOH · (H₂O)₂ complexes formed along with tetramers; at a double excess of H₂O, the components of the solution were completely bound into these trimers. In dilute solutions (from 0 to 3.6 M CF₃COOH), the acid is completely dissociated into H₅O₂⁺ and CF₃COO^– ions hydrated with water molecules. In the range of medium concentrations (from 3.6 M to [H₂O]/[CF₃COOH] = 2: 1), the solutions contain both these ions and CF₃COOH · (H₂O)₂ dihydrates. For this range of compositions of the CF₃COOH−H₂O system, the concentrations of H₅O₂⁺ ions and CF₃COOH · (H₂O)₂ dihydrates were calculated.

The conditions are determined, and the parameters for the onset of the mode of dimeric molecular association in the water system are estimated. The characteristics of dimeric associates of molecules are determined. The region of anomalous thermal compression water is increased from T ≤ 4°C to T ≤ 66.4°C by introducing the temperature equivalent T₀ of the energy of proton transition from molecule to molecule into the parameter of resonant interaction of atoms of different molecules. The time of transfer of excitation energy correlates with the periods of the valence and deformation vibrations of the molecules. Therefore, a molecule that performs valence vibrations “has time” to store an excitation energy sufficient to provide a parallel orientation of the spins of the nuclei of the hydrogen atoms in the molecules. Molecules that perform deformation vibrations have zero spins because of the smallness of the frequencies of such vibrations.

A plug flow reactor operating on a heterogeneous liquid−liquid system in which an exothermic bimolecular reaction takes place is modeled. The effect of the main governing parameters (Peclet and Damkheler numbers and a dimensionless parameter P characterizing mass transfer between the liquid phases) on the thermal modes of the reactor is examined. Depending on the values of these parameters, one or three steady states can be realized in the reactor. It is established that, with increasing parameter P, the region of multiplicity of steady states expands and shift toward lower values of the Damkohler number. The phenomenon of hysteresis is observed in the region of multiplicity of steady states.

The aim of this work was to perform a comparative study of the well-known models of physicochemical processes based on the dissociation of oxygen as an example. The comparison was conducted with the use of the available results of calculations obtained by a method of quasi-classical trajectories. The principle of the information provision of models and the complexity of their computational implementation were taken into account in the study. The dissociation process was considered in the framework of one-temperature, two-temperature, and level approximations. The MD Trajectory software was used for the simulation of molecular reaction dynamics. Computer experiments with theoretical models were carried out using an Internet catalog of physical and chemical process models. A modification of the Marrone–Treanor level model was proposed for the approximation of the rate constant of oxygen dissociation obtained by the method of quasi-classical trajectories in the level approximation. The empirical parameter of this model was replaced by a new parameter, which took into account its possible dependence on translational temperature. For a two-temperature approximation, recommendations were formulated in terms of the applicability ranges of the models taking into account the vibrational temperature of dissociating molecules based on a comparison of the results of trajectory calculations and theoretical models. The results of trajectory calculations and theoretical models in a two-temperature approximation were also compared with the available experimental data on the dissociation of oxygen molecules.

A mathematical model of the exothermic chemical transformation of a high-calorie mixture in the presence of centrifugal forces is considered. The process is studied for the 3NiO + (2 + α)Al → Al₂O₃ + (3 − α)Ni + αNiAl thermite composition, as an example. Such processes are used in high-temperature synthesis for the production of target products in the combustion wave propagating through the initial mixture. This technological process represents a combination of high-temperature combustion with the formation of liquid products, their separation, and subsequent cooling. A distinctive feature of the proposed model is the use of a “through” description, which makes it possible to examine the mutual influence of the individual stages on the dynamics of the process. This feature provides a more realistic description of the actual process.

The effect of the initial temperature on the characteristics of the shot is studied for high-density block charges prepared by pressing powder grains coated with a polymer film. The experiments were carried out on laboratory barrel setups of caliber 7.62 and 14.5 mm with recording the muzzle velocity and pressure. Two shot schemes are considered: a classical scheme with the block charge placed in the chamber, and a hybrid scheme, with the block charge attached to the projectile, burning as it travels along the barrel. The effect observed at various initial temperatures of the block charge is compared with similar data for a standard poured-powder charge, for which the temperature gradient within ±50°C is 2.1−2.5% per 10°C. The experiments showed that, at positive temperatures, the temperature gradient for block propellant charges is appreciably smaller, 0.9−1.2% for the traditional shot scheme and 0.8% for the hybrid scheme. At negative temperatures of the block propellant charges, the characteristics of the shot decline significantly, which, however, can be restored to the temperature gradient typical of the standard shot by boosting the igniter.

The forced ignition, combustion, and spontaneous ignition of a drop of n-dodecane in an atmosphere of air at a normal pressure under microgravity conditions were studied based on a physicomathematical model of drop combustion and a detailed kinetic mechanism of the oxidation and combustion of n-dodecane C₁₂H₂₆. The selection of n-dodecane was related to the Russian–American experiment CFI (Cool Flame Investigation) Zarevo performed in 2017 aboard the International Space Station with the use of the large drops of this hydrocarbon. The analysis carried out deepens our knowledge about the flameless combustion of a large drop under the conditions of microgravity. The calculations showed that, after the radiation extinction of a hot flame, the drop can continue to evaporate because of the exothermic low-temperature oxidation of fuel vapor with repeated blue flame flashes at a characteristic temperature of 980–1000 K. A detailed analysis of the calculation results showed that the regular splashes of temperature resulted from the thermal decomposition of hydrogen peroxide—branching with the release of hydroxyl radicals.

A rigorous calculation of the thermodynamic equilibrium of the metal–external charge system has shown that the generally accepted assumption that the electric field does not penetrate into the metal is incorrect. In reality, the field penetrates deep into the metal, and the interaction of the charge with the metal is noticeably stronger than the standard interaction with the electric image of the charge. It depends on the characteristics of the electronic system of the metal, on the sign of the charge, and, somewhat differently than the standard one, depends on the magnitude of the charge.

This work was devoted to the acquisition and analysis of information on the charge state of polyprotonated and polycationated biomolecules based on experimental mass-spectrometric data obtained using the electrospray ionization of the solutions of biopolymers. This was performed by solving an inverse problem for the calculation of the probabilities of the retention of protons and sodium ions by the ionogenic groups of the biomolecules of cytochrome c from equine horse. A probabilistic model and the theoretical description of an algorithm for the two-dimensional decomposition of charge distributions are given. This is a new approach, which does not have analogs in the publications of other authors. The results of calculations performed according to the developed programs—the two-dimensional and one-dimensional decomposition of charge distributions with the selection of components corresponding to structurally homogeneous ions—are discussed.

The possibility of adsorption of pollutant gas molecules on the surface of polyacrylonitrile subjected to thermal treatment at 300–600°С was studied theoretically. The theoretical modeling was performed by quantum chemical calculations and molecular modeling. The results of modeling showed that annealed polyacrylonitrile exhibits gas sensitivity in reactions with chlorine and nitrogen dioxide.

Structural dynamic analysis combining IR spectroscopy, DSC, and EPR spectroscopy is applied to studying films based on chlorinated natural rubber (CNR), butadiene nitrile rubber (BNR), and blends thereof. The influence of various solvents, such as methyl ethyl ketone (MEK), ethyl acetate (EA), methyl acetate (MA), and acetone (A), on the structure and molecular dynamics (τ) of CNR/BNR polymer films is examined. The strongest changes in the molecular mobility (τ) and the glass transition temperature (T_gt) relative to those of the starting materials are observed for the 50: 50% CNR/BNR blends prepared using all the solvents (except for acetone, the maximum values of τ for which is observed at a ratio of CNR: BNR = 80: 20%), which can be explained by the inversion of phases in the blends. Annealing at 140°С causes an increase in the correlation time of the probe, and, consequently, a decrease in the molecular mobility, which is due to the intermolecular crosslinking of the components.

The thermal decomposition of polyethylene and butadiene rubber chains in the presence of a tensile force acting along the axis of the molecule was simulated. The reaction of an isolated chain was considered. The chain models were the octane and 2,6-octadiene molecules. A deformation was introduced in the problem by fixing nonequilibrium distances between the terminal carbon atoms. The reaction coordinate (the middle C–C bond length R) was scanned at a fixed length of the molecule (L). That is, the potential energy surface section of the reaction was constructed at L = const. The reaction sensitivity to deformation was evaluated by B3LYP, LC-ωPBE, CCSD(T), CASSCF, and MP2 quantum-chemical calculations. All these calculations showed that the molecule elongated by ~1 Å for polyethylene, but shortened by 0.3–0.5 Å for 2,6-octadiene during chain scission. This means that the tensile deformation accelerates the decomposition of polyethylene, but decelerates the decomposition of butadiene rubber.

The adsorption and interaction of hydrogen, carbon monoxide, and oxygen with gold and nickel nanoparticles is studied by scanning tunneling microscopy and spectroscopy. It is established that the HCO radical is formed on gold nanoparticles by the reaction between adsorbed H₂ and CO, which is subsequently oxidized by oxygen to water and CO₂. At the same time, after exposure to H₂ and CO, nickel nanoparticles coated with oxide are reduced. The formation of adsorbed HCO on such nanoparticles is not observed.

The TiO₂/MoO₃ and TiO₂/V₂O₅ thin-film nanoheterogeneous photocatalysts obtained by mechanochemical activation of oxides were studied by using the test reactions of probing dye photooxidation, EPR spectroscopy, X-ray diffraction, and atomic force microscopy. It was shown that mechanochemical synthesis yields nanoheterostructures of the oxide–oxide type, in which optimum conditions were created for photogeneration of charge carriers and their accumulation and thus opens up an opportunity of obtaining photocatalytic systems with prolonged oxidative activity.

With the purpose of improving the method for the in-place-repair of the surfaces of machinery parts and reducing friction and wear parameters due to the action of a reductive lubricating composition (RLC), the mechanism of the transformation and transfer of contact layers in the bulk of the lubricating medium between the RLC components and the reconstructed surface is studied. A hypothesis of how the contact layers of the lubricating medium are transformed and transferred and are consecutively subjected to deformation, shear, and removal into the bulk, being then replaced by new contact layers of lubricating medium, is put forward. A theoretical analysis shows that the most important factors for increasing the efficiency of RLC are the structuring of the lubricating medium by nanosized metallic elements and the selective aggregation and removal of wear products and oil oxidation products on a filter. These conditions are provided by increasing the effectiveness of the traditional RLC and other additives and by introducing into the lubricating medium a mixture of nitrogen-containing components, such as ammonium hydroxide and urea. Adding the modified oil composition into commercial oil makes it possible to double its repair-recovery and antiwear capabilities. The additives proposed are effective at low dosages (3 vol % in oil), being, in addition, nontoxic and posing no hazard when handled and transported.

The uptake of NO₃ on a pyrene coating at [NO₃] = 2.5 × 10¹²–1.2 × 10¹³ cm⁻³ is studied using a coated-insert flow tube reactor coupled to a mass spectrometer. It is established that, in this concentration range, the uptake occurs by the impact recombination mechanism, whereas the consumption of surface sites involves the unimolecular decomposition of stabilized surface complexes. Several hundreds of NO₃ radicals are consumed per surface site destroyed. The uptake coefficient depends on the exposure time, being described by the expression γ(t) = γ₀exp(−t/τ), where γ₀ and τ are parameters dependent on the NO₃ concentration. Based on the Langmuir adsorption concept, the following elementary parameters determining the uptake process are estimated: the Langmuir coefficient, K_L = 7.1 × 10⁻¹³ cm³; the desorption rate constant, k_d = 44 s⁻¹; and the rate constant for the unimolecular heterogeneous conversion of surface complexes, k_r = 6.6 × 10⁻² s⁻¹. Gas chromatography–mass spectrometry measurements showed that the main products of the reaction are phthalates. The nitropyrene yield is found to be ~0.6%.